Alone in the Dark created the Survival/Horror genre, Resident Evil perfected it and made it a viable genre, and that allowed Silent Hill to get funded.

But Silent Hill did things way too different from Resident Evil, and at the end what matter is the end result of the product. Just because they are in the same genre, or that they got similar influences (which they didn't) doesn't mean that they are the same thing.

With FFX no game previously enabled you to change characters in battle on the fly

Breath of Fire IV.

BoF4 did a better job of it as well. Sure, you had to switch party members to hit monsters' weaknesses in Final Fantasy X, but Breath of Fire IV had a neat little combo system and the people in the back row actually did something, like cheer the people in the front row on.

How did any of those games mimic FFX in a way that FFX didn't mimic some other game in?

Being influential and being original are two different things. Doom clearly aped Wolfenstein, but nevertheless, it was Doom that brought the FPS genre to the mainstream, and thus new FPS games were called "Doom clones" for years.

Just because FFX didn't invent the things it made popular doesn't mean it wasn't influential. That's pretty much how everything works. A concept will be around for years, and then all it takes is one high profile game, TV show or band to come along and get so much success that everyone starts to imitate them, neither knowing nor caring that they weren't the originators.